Light pipe light source with flux condensing light pipe

ABSTRACT

An optical device for increasing the brightness of electromagnetic radiation emitted by a source by folding the electromagnetic radiation back on itself. The source of electromagnetic radiation has a first width, a first input end of a first light pipe has a second width, and a second input end of a second light pipe has a third width. An output end of the first light pipe may be reflective; while an output end of the second light pipe may be transmissive. The source is located substantially proximate to a first focal point of a reflector to produce rays of radiation that reflect from the reflector and substantially converge at a second focal point; and the input ends of the first and second light pipes are located proximate to the second focal point to collect the electromagnetic radiation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of Application Ser. No. 09/983,213,filed Oct. 23, 2001, now U.S. Pat. No. 6,565,235, which claims thebenefit of U.S. Provisional Application Ser. No. 60/243,280, filed Oct.26, 2000, the disclosure of which is incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to increasing the brightness of an arc lamp byfolding the arc back into itself.

2. Description of the Related Art

U.S. patent application Ser. No. 09/604,921, the disclosure of which isincorporated by reference, describes a dual-paraboloid reflector systemthat may be used to couple light from an arc lamp into a target such asa standard waveguide, e.g., a single fiber or fiber bundle, or outputelectromagnetic radiation to the homogenizer of a projector. Thisoptical collection and condensing system, as illustrated in FIG. 1, usestwo generally symmetric paraboloid reflectors 10, 11 that are positionedso that light reflected from the first reflector 10 is received in acorresponding section of the second reflector 11. In particular, lightemitted from a light source 12, such as an arc lamp, is collected by thefirst parabolic reflector 10 and collimated along the optical axistoward the second reflector 11. The second reflector 11 receives thecollimated beam of light and focuses this light at the target 13positioned at the focal point.

The optical system of FIG. 1 may employ a retro-reflector 14 inconjunction with the first paraboloid reflector 10 to capture radiationemitted by the light source 12 in a direction away from the firstparaboloid reflector 10 and reflect the captured radiation back throughthe light source 12. In particular, the retro-reflector 14 has agenerally spherical shape with a focus located substantially near thelight source 12 (i.e., at the focal point of the first paraboloidreflector) toward the first paraboloid reflector to thereby increase theintensity of the collimated rays reflected therefrom.

U.S. application Ser. No. 09/669,841, the disclosure of which isincorporated by reference, describes a dual ellipsoidal reflector systemthat may be used to couple light from an arc lamp into a target. Thisoptical collection and condensing system, as illustrated in FIG. 2, usestwo generally symmetric ellipsoid reflectors 20, 21 that are positionedso that light reflected from the first reflector 20 is received in acorresponding section of the second reflector 21. In particular, lightemitted from the light source 22 is collected by the first ellipticalreflector 20 and collimated along the optical axis 25 toward the secondreflector 21. The second reflector 21 receives the collimated beam oflight and focuses this light at the target 23 positioned at the focalpoint.

The objective of the above-described systems that collect, condense, andcouple electromagnetic radiation into a target is to maximize thebrightness of the electromagnetic radiation at the target. These systemsmust be efficient and have relatively long useful lives.

Arc lamps, e.g., metal halide lamps, xenon lamps, or high pressuremercury lamps, are often used in the above-mentioned systems as sourcesof light. One of the means by which high brightness may be obtained isby making the arc gap in the lamp small such that all the light isemitted from a small spot. An ideal source is a point source, in whichthe distance between the electrodes is negligible. There are practicallimitations, however, to reducing the distance between the electrodesbelow a certain value. Among the limitations associated with a shorterarc are a loss of emission efficiency and reduced electrode life. Theuseful lives of the electrodes will be shorter with the shorter arc.

Since arc lamp gaps cannot be reduced indefinitely, there remains a needto increase the brightness of the electromagnetic radiation emitted byarc lamps with longer gaps for coupling into a target.

SUMMARY

An optical device is provided for increasing the brightness ofelectromagnetic radiation emitted by a source and coupled into a targetby folding the electromagnetic radiation back on itself. The opticaldevice includes the source of electromagnetic radiation, which has afirst width; a first light pipe with a first input end and a reflectiveend, the first input end having a second width; a second light pipedisposed parallel to the first light pipe, the second light pipe furtherhaving a second input end juxtaposed to the first input end of the firstlight pipe and an output end, the second input end having a third width;a first reflector having a first optical axis and a first focal point onthe first optical axis; and a second reflector having a second opticalaxis and a second focal point on the second optical axis disposedsubstantially symmetrically to the first reflector such that the firstoptical axis is substantially collinear with the second optical axis.The source is located substantially proximate to the first focal pointof the first reflector to produce rays of radiation that reflect fromthe first reflector to the second reflector and substantially convergeat the second focal point; and the input ends of the first and secondlight pipes are located proximate to the second focal point of thesecond reflector to collect the electromagnetic radiation. The firstwidth is substantially equal to or smaller than the sum of the secondand the third widths.

The above and other features and advantages of the present inventionwill be further understood from the following description of thepreferred embodiments thereof, taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a collecting and condensing apparatususing paraboloid reflectors for use with an embodiment of the invention;

FIG. 2 is a schematic diagram of a collecting and condensing apparatususing ellipsoid reflectors for use with an embodiment of the invention;

FIG. 3 is a schematic diagram of an optical device for foldingelectromagnetic radiation emitted by a source back on itself accordingto a first embodiment of the invention;

FIG. 4(a) is a detail of the light pipes shown in the embodiment of FIG.3;

FIG. 4(b) is an embodiment of the light pipes shown in FIG. 4(a) withdifferent lengths;

FIG. 5 is the embodiment shown in FIG. 3 outputting to a waveguide; and

FIG. 6 is the embodiment shown in FIG. 3 outputting to a projectionsystem; and

FIG. 7 a schematic diagram of an optical device for foldingelectromagnetic radiation emitted by a source back on itself accordingto a second embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 3 is shown a first embodiment of a collecting and condensingapparatus 300. The apparatus includes a source 301 of electromagneticradiation 302 having a first width 303. In a preferred embodiment,source 301 is a light-emitting arc lamp. Source 301 may be, e.g., axenon lamp, a metal halide lamp, an HID lamp, or a mercury lamp. Source301 may be, in the alternative, a filament lamp.

If source 301 were an arc lamp, width 303 would be the linear distancebetween its electrodes, for an AC lamp, or between its anode and itscathode, for a DC lamp. If source 301 were a filament lamp, first width303 would be the hot length of the filament, e.g. between the leads.

A first light pipe 304 with a first input end 305 and a reflective end306 is disposed parallel to a second light pipe 307 with a second inputend 308 and an output end 309. First input end 305 and second input end308 are juxtaposed. Reflective end 406 and output end 409 may also bejuxtaposed, if, e.g., first light pipe 404 and second light pipe 407 areof similar lengths, as shown in FIG. 4(a), although this is not strictlynecessary. Light pipe 417 can be, e.g., longer than light pipe 414, asshown in FIG. 4(b). The first input end 305 has a second width 310,while the second input end 308 has a third width 311.

If first light pipe 304 and second light pipe 307 have substantiallyrectangular cross-sections, then second width 310 and third width 311are dimensions of first input end 305 and second input end 308,respectively, measured in a particular direction. In a preferredembodiment, first light pipe 304 and second light pipe 307 are bothsubstantially tapered light pipes. First light pipe 304 and second lightpipe 307 may be made of, e.g., quartz, glass, plastic, or acrylic.

A first reflector 312 having a first optical axis 313 and a first focalpoint 314 on first optical axis 313 is placed substantiallysymmetrically to a second reflector 315 having a second optical axis 316and a second focal point 317. First optical axis 313 is substantiallycollinear with second optical axis 316. There is a plane of symmetrywith respect to first and second reflectors 312 and 315 that is normalto optical axes 313 and 316. Thus second reflector 315 may be formed bymirroring first reflector 312 through the plane of symmetry.

In one embodiment, first and second reflectors 312 and 315 have acoating that reflects only a pre-specified portion of theelectromagnetic radiation spectrum. In a preferred embodiment, thecoating only reflects visible light radiation, a pre-specified band ofradiation, or a specific color of radiation.

In a preferred embodiment, first and second reflectors 312 and 315 areeach at least a portion of a substantially paraboioidal surface ofrevolution. In other, less preferred embodiments, first and secondreflectors 312 and 315 are each at least a portion of a substantiallytoroidal, spheroidal, hyperboloidal, or ellipsoidal surface ofrevolution.

Source 301 is located substantially proximate to first focal point 314of first reflector 312 to produce rays of radiation 302 that reflectfrom first reflector 312 to second reflector 315 and substantiallyconverge at second focal point 316. First and second input ends 305 and308 are located substantially proximate to second focal point 317 ofsecond reflector 315 to collect electromagnetic radiation 302. Sincefirst input end 305 and second input end 308 are juxtaposed, secondwidth 310 and third width 311 may be oriented end-to-end, such that theyform a line. The line along which second width 310 and third width 311are oriented may be substantially parallel to first width 303, i.e. thedirection from one electrode of source 301 to the other.

In a preferred embodiment, first width 303 is substantially equal to thesum of second width 310 and third width 311. First width 303, however,may be smaller or larger than the sum of second width 310 and thirdwidth 311, albeit with reduced efficiency. As shown in FIG. 4(a), secondwidth 310 and third width 311 may be in any ratio, as long as their sumequals substantially first width 303. Second width 310 may be, e.g.,substantially equal to third width 311, or second width 310 may besubstantially equal to twice third width 311.

A portion of the electromagnetic radiation 302 emitted by source 301impinges directly on first reflector 312 and a portion of theelectromagnetic radiation 302 does not impinge directly on firstreflector 312. To collect the electromagnetic radiation 302 that doesnot impinge directly on first reflector 312, system 300 includes anadditional reflector 321 constructed and arranged to reflect at leastpart of the portion of the electromagnetic radiation 302 that does notimpinge directly on first reflector 312 toward first reflector 312through first focal point 314 of first reflector 312 to increase theflux intensity of the converging rays.

In a preferred embodiment, additional reflector 321 is a sphericalretro-reflector disposed on a side of source 301 opposite firstreflector 312 to reflect electromagnetic radiation 302 emitted fromsource in a direction away from first reflector 312 toward firstreflector 312 through the first focal point 314 of first reflector 312.

Since first input end 305 and second input end 308 are juxtaposed atsecond focal point 316, rays of radiation 302 converging on first inputend 305 and second input end 308 will have approximately the samedimensions as the rays of radiation 302 emitted from source 301. Sincefirst width 303 is substantially equal to the sum of second width 310and third width 311, rays of radiation 302 will be distributed to firstinput end 305 and second input end 308 in proportion to the ratio ofsecond width 310 to third width 311. Thus, a portion of rays ofradiation 302 will be coupled into first light pipe 304, while thebalance will be coupled into second light pipe 307.

The portion of rays of radiation 302 coupled into second light pipe 307will travel through second light pipe 307 and emerge from output end309. Meanwhile, the portion of rays of radiation 302 coupled into firstlight pipe 304 will be reflected at reflective end 306 andre-transmitted through first light pipe 304, emerging at first input end305. The rays emergent from first input end 305 will be reflected bysecond reflector 315 toward first reflector 312, converging at firstfocal point 314. These convergent rays will then pass through the arcgap to be reflected in turn by additional reflector 321 toward firstreflector 312, rejoining the other rays on their way to be coupled intothe target. Some of this radiation will be coupled into second lightpipe 307 and emerge from output end 309. Thus, the rays of radiation 302emitted by source 301 with an arc gap of first width 303 end up beingfocused on a spot smaller than first width 303.

In an alternative embodiment, shown in FIG. 5, a waveguide 318 may bedisposed substantially proximate to output end 509 of second light pipe507. Waveguide 318 may be, e.g., a single core optic fiber, a fiberbundle, a fused fiber bundle, a polygonal rod, a hollow reflective lightpipe, or a homogenizer. A cross-section of waveguide 318 may be that ofa circular waveguide, a polygonal waveguide, a tapered waveguide or acombinations thereof. In another alternative embodiment, waveguide 318may be a fiber optic.

In another alternative embodiment, shown in FIG. 6, a condenser lens 319may be disposed substantially proximate to output end 709 of secondlight pipe 707. An image projection system 320 may be disposedsubstantially proximate to an output side of condenser lens 319 toilluminate an image by releasing the collected and condensed radiationto display the image.

In FIG. 7 is shown a second embodiment of a collecting and condensingapparatus 600. Collecting and condensing apparatus 600 is similar tocollecting and condensing apparatus 300 with the exception of theorientation and generating curve of the reflectors.

A first reflector 612 having a first optical axis 613 and a first focalpoint 614 on first optical axis 613 is placed substantiallysymmetrically to a second reflector 615 having a second optical axis 616and a second focal point 617. First optical axis 613 is substantiallycollinear with second optical axis 616. There are two planes ofsymmetry, one of which is normal to optical axes 613 and 616, while theother is normal to the first plane of symmetry and contains optical axes613 and 616. First reflector 612 is thus substantially symmetrical tosecond reflector 615 in that first reflector 612 is just secondreflector 615 mirrored through the two planes of symmetry, in eitherorder.

In a preferred embodiment, first and second reflectors 612 and 615 areeach at least a portion of a substantially ellipsoidal surface ofrevolution. In other, less preferred embodiments, first and secondreflectors 612 and 615 are each at least a portion of a substantiallytoroidal, spheroidal, or paraboloidal surfaces of revolution.

Since first input end 605 and second input end 608 are juxtaposed atsecond focal point 616, rays of radiation 602 converging on first inputend 605 and second input end 608 will have approximately the samedimensions as the rays of radiation 602 emitted from source 601. Sincefirst width 603 is substantially equal to the sum of second width 610and third width 611, rays of radiation 602 will be distributed to firstinput end 605 and second input end 608 in proportion to the ratio ofsecond width 610 to third width 611. Thus, a portion of rays ofradiation 602 will be coupled into first light pipe 604, while thebalance will be coupled into second light pipe 607.

The portion of rays of radiation 602 coupled into second light pipe 607will travel through second light pipe 607 and emerge from output end609. Meanwhile, the portion of rays of radiation 602 coupled into firstlight pipe 604 will be reflected at reflective end 606 andre-transmitted through first light pipe 604, emerging at first input end605. The rays emergent from first input end 605 will be reflected bysecond reflector 615 toward first reflector 612, converging at firstfocal point 614. These convergent rays will then pass through the arcgap to be reflected in turn by additional reflector 619 toward firstreflector 612, rejoining the other rays on their way to be coupled intothe target. Some of this radiation will be coupled into second lightpipe 607 and emerge from output end 609. Thus, the rays of radiation 602emitted by source 601 with an arc gap of first width 603 end up beingfocused on a spot smaller than first width 603.

A method of folding electromagnetic radiation emitted by a source backon itself to increase the brightness of the source is as follows. Asource of electromagnetic radiation having a first width is positionedat a focal point of a first reflector. Rays of radiation are produced bythe source. The rays of radiation are reflected by the first reflectortoward a second reflector. The rays of radiation converge at a focalpoint of the second reflector. A first light pipe having a first inputend and a reflective end, the first input end further having a secondwidth, and a second light pipe having an second input end and an outputend, the second input end further having a third width, is positionedsuch that the first and second input ends are substantially proximate tothe focal point of the second reflector, and such that the first widthis substantially equal to a sum of the second and third widths. The raysof radiation reflected by the second reflector pass through the firstand second input ends of the first and second light pipes, insubstantial proportion to the ratio of the second width to the thirdwidth. Rays of radiation passing through the second light pipe areoutput. Rays of radiation passing through the first light pipe arereflected back toward the second and first reflectors, to said source.

While the invention has been described in detail above, the invention isnot intended to be limited to the specific embodiments as described. Itis evident that those skilled in the art may now make numerous uses andmodifications of and departures from the specific embodiments describedherein without departing from the inventive concepts.

1. A collecting and condensing apparatus comprising: a source ofelectromagnetic radiation, said source having a first width; a firstlight pipe, said first light pipe having a first input end and areflective end, said input end having a second width; a second lightpipe disposed substantially parallel to said first light pipe, saidsecond light pipe having a second input end and an output end, saidsecond input end having a third width; said source producing rays ofradiation; and wherein said first input end of said light pipe islocated in substantial proximity to said second input end of said lightpipe to collect said electromagnetic radiation.
 2. The collecting andcondensing apparatus of claim 1, wherein said first width issubstantially equal to the sum of said second and said third widths. 3.The collecting and condensing apparatus of claim 1, wherein said firstwidth is smaller than the sum of said second and said third widths. 4.The collecting and condensing apparatus of claim 1, wherein said firstwidth is larger than the sum of said second and said third widths. 5.The collecting and condensing apparatus of claim 1, wherein said secondwidth is substantially equal to said third width.
 6. The collecting andcondensing apparatus of claim 1, wherein said second width issubstantially twice said third width.
 7. The collecting and condensingapparatus of claim 1, wherein said first and said second light pipescomprise substantially tapered light pipes.
 8. The collecting andcondensing apparatus of claim 1, wherein said source comprises afilament lamp.
 9. The collecting and condensing apparatus of claim 1,further comprising a waveguide disposed substantially proximate to saidoutput end of said second light pipe, said waveguide selected from thegroup consisting of a single core optic fiber, a fiber bundle, a fusedfiber bundle, a polygonal rod, a hollow reflective light pipe, or ahomogenizer.
 10. The collecting and condensing apparatus of claim 1,wherein said source comprises a light-emitting arc lamp.
 11. Thecollecting and condensing apparatus of claim 10, wherein said arc lampcomprises a lamp selected from the group comprising a xenon lamp, ametal halide lamp, an HID lamp, a mercury lamp, or a high-pressuremercury lamp.
 12. A system of folding electromagnetic radiation back onitself comprising: means for producing rays of radiation; first meansfor integrating said rays of radiation; first means for reflecting saidintegrated rays of radiation back through said first integrating means;second means for reflecting said integrated rays of radiation; secondmeans for further integrating said integrated rays of radiation; andmeans for outputting said further integrated rays of radiation.
 13. Amethod of folding electromagnetic radiation back on itself to preservebrightness, the method comprising: positioning a source ofelectromagnetic radiation having a first width at a first focal point ofa reflector; producing rays of radiation by said source; reflecting saidrays of radiation by said reflector toward a second focal point;converging said rays of radiation at said second focal point of saidreflector; positioning a first light pipe having a first input end and areflective end, said first input end further having a second width, anda second light pipe having an second input end and an output end, saidsecond input end further having a third width, such that said first andsecond input ends are substantially proximate to said second focalpoint, and wherein said first width is substantially equal to a sum ofsaid second and third widths; and passing the rays of radiationreflected by said reflector through said first and second input ends ofsaid first and second light pipes; outputting rays of radiation passingthrough said second light pipe; and reflecting rays of radiation passingthrough said first light pipe back toward said reflector and saidsource.